Since diamond has a large band gap, it has been known to use a diamond single crystal film as a light receiving portion of a UV-sensor element. For example, it has been known so far to manufacture a diamond single crystal film the surface of which is substantially covered with hydrogen atoms (hereinafter also referred to as “hydrogenation”) by a microwave-excited plasma vapor deposition method using methane and a hydrogen gas and utilize the same as a light receiving portion (for example, refer to Patent documents 1, 2). Further, as another example, a diamond film UV-sensor having a UV detection layer in which oxygen is chemically adsorbed to the surface of a diamond film oriented and grown monoaxially by vapor phase synthesis (hereinafter also referred to as “oxygenation”) has also been proposed (for example, refer to Patent document 3).
By the way, an important index of a light receiving portion material in the UV sensor element includes a ratio between the value of a photocurrent flowing under UV irradiation and a value of photocurrent flowing under the irradiation of a visible light (hereinafter also referred to as “UV/visible light blind ratio”). Since a UV sensor element of higher sensitivity can be attained as the value is larger, it is actually demanded to have a larger value.    Patent Document 1: JP-A No. 2005-310963    Patent Document 2: JP-A No. 11(1999)-097721    Patent Document 3: JP-A No. 11(1999)-248531